The invention relates to a device for turning sheets in a sheet-fed rotary printing machine in which the device has a storage drum for handling sheets and a turning drum disposed downstream of the storage drum for turning the sheets.
German Patent DE 44 24 968 C2 discloses a turning device of the type discussed above which has a storage drum, on the outer lateral surface of which a plurality of sheets are held. In a direction of movement of the sheets, a turning drum, which has a holding device for engaging a rear edge of the sheet to be turned, is disposed downstream of the storage drum. The configuration of the storage drum and the turning drum is selected such that their lateral surfaces virtually touch one another at a tangent point. The storage drum has a first blowing device, with the aid of which a stream of blast air can be applied to the sheet which has already been taken hold of by the holding device, in order to press the sheet off the storage drum, assisting with the operation of turning the sheet. Moreover, to assist with the turning operation, a second blowing device is provided above the tangent point, with the aid of which air can be blown into the tangent point in order to press the sheet to be turned downward and thus to assist with detaching the sheet from the storage drum.
By detaching the sheet to be turned from the circumference of the storage drum and conveying it onward with the aid of the turning drum, air situated in the turning area is entrained by the sheet, resulting in a local pressure reduction which acts on the next sheet, which is held on the circumferential surface of the storage drum with the aid of the holding device and as a result may be at least partially lifted off the storage drum. Consequently, an in-register transfer of the sheets from the storage drum to the turning drum cannot be ensured in all cases. This occurs because, when turning the rear edge of sheets, to ensure an in-register transfer of the sheet stored on the storage drum, in particular in the case of face-side printing and perfecting, it is necessary to produce precise conditions for the entire path of the stored sheet. For this purpose, the sheet is usually clamped on the storage drum surface at the rear edge by clamping suckers, so that all the sheets come to rest in exactly the same position during the storage operation. In the case of half-turn storage drums, the uniformity of the two halves of the storage drum is ensured by an accurately ground surface. However, perfect transfer of the sheet stored in this way is only ensured if the sheet can be held in this state or position by the clamping suckers. However, this is not the case with a high printing capacity, which may, for example, amount to 15,000 sheets per hour.
With a printing capacity which is as high as this, with only approximately 0.1 second between the instant at which the leading sheet is detached and that at which the next sheet enters the reduced-pressure zone, it is impossible for sufficient air to flow into the reduced-pressure zone which is formed between the turning drum and the storage drum in the space between the turning drum and the storage drum. The blast streams from the first and second blowing devices of the known turning device, which serve to assist with the turning operation, cannot sufficiently reduce the pressure reduction which is active in the turning area, since the blast-air stream of the second blowing device disposed above the tangent point, owing to the very small space between the storage drum and the turning drum, can only reach the turning area lying beneath the tangent point in a weakened form, if at all. The first blowing device disposed in the storage drum is only active for a very short time in order to lift the sheet resting on the storage drum at its rear-edge area. Also, the pressure differences that are customary with blast air and the outlet cross sections of the blowing nozzles are too small to compensate for the pressure reduction that is generated.
It is accordingly an object of the invention to provide devices for turning sheets in a sheet-fed rotary printing machine which overcome the above-mentioned disadvantages of the prior art devices of this general type, in which an in-register transfer of the sheet stored on the circumferential surface of the storage drum can be ensured even at a high press speed.
With the foregoing and other objects in view there is provided, in accordance with the invention, a sheet turning device for a sheet-fed rotary printing machine. The sheet turning device is formed of a storage drum for handling at least two sheets and has at least one holding device for each of the sheets; and a turning drum disposed downstream of the storage drum and has at least one holding device for engaging a rear edge of a sheet of the sheets to be turned. An operation of detaching the sheet to be turned from the storage drum and carrying it along by the turning drum leads to a formation of a pressure reduction in a reduced-pressure area formed between the sheet to be turned, the storage drum and the turning drum. The turning drum has a lateral surface with at least one channel formed therein in which air can be at least one of sucked from and blown into the reduced-pressure area.
The device is distinguished by the fact that at least one channel and/or at least one passage orifice is connected to an inner chamber of the turning drum, via which channel and/or passage orifice air can be sucked and/or blown into the reduced-pressure area. A free cross section of flow of the channel running, for example, in the circumferential direction of the turning drum and, if appropriate, that of the passage orifice are sufficiently large for a pressure reduction which is formed in the area between the storage drum. The turning drum and the sheet to be turned as a result of the sheet to be turned being detached from the storage drum and as a result of the turning operation to be able to suck in at least enough air through the channel and/or the passage orifice for it to be possible to prevent the next sheet, which is resting on the outer circumferential surface of the storage drum, from being lifted off. In this variant, it is possible to dispense with blowing devices which supply blast air and/or compressed air to the reduced-pressure area, a fact which simplifies the structure of the turning device. In another variant, at least one blast-air/compressed-air supply device is provided, which, by way of example, supplies the inner chamber of the turning drum with blast air or compressed air which passes via the passage orifice in the turning-drum lateral surface, into the reduced-pressure area. The at least one passage orifice is disposed downstreamxe2x80x94as seen in the direction of rotation of the turning drumxe2x80x94of the holding device which holds the rear edge of the sheet to be turned and is provided on the turning drum. As an alternative or in addition, it is also possible for a blast-air/compressed-air stream to be introduced into the reduced-pressure area via the channel. A common feature of all these exemplary embodiments is that the incoming flow of air via the channel and/or the passage orifice into the reduced-pressure area is at least assisted by the pressure reduction acting in that area.
According to a refinement of the invention, at least one wall of the channel is formed at least in part by a flattened section made in the lateral surface of the turning drum. In connection with the present invention, the term xe2x80x9cflattened sectionxe2x80x9d is understood as meaning a planar or substantially planar area on a circular or curved surface. In an advantageous embodiment, the turning drum, in the region of the flattened section, has for the most part a substantially round cross section, the channel wall having a different, preferably smaller radius of curvature, at least in its area disposed upstream of the flattened sectionxe2x80x94as seen in the direction of flow of the airxe2x80x94from the turning drum.
In accordance with an added feature of the invention, the holding device of the turning drum has at least one gripper disposed on the flattened section.
In accordance with an additional feature of the invention, the turning drum has a circumference, and the channel formed in the lateral surface of the turning drum runs over region of the circumference of the turning drum.
In a further embodiment, the device is distinguished by the fact that at least one open-edged recess, at least one channel and/or at least one passage orifice connected to an inner chamber of the storage drum is/are provided in the lateral surface of the storage drum. Via the recess, channel and/or passage orifice air can be introduced into the reduced-pressure area. The recess, which may, for example, extend over the entire length of the storage drum, is closed laterally, i.e. toward the edge of the machine, and in the circumferential direction at least to a sufficient extent for it to be impossible for air which has been blown in from its open side to escape. The xe2x80x9cair cushionxe2x80x9d, which has been introduced into the recess and is introduced into the reduced-pressure area with the aid of at least one blowing device immediately before entry into the recess, is sucked out of the recess in the turning area by the reduced pressure prevailing in that area, with the result that the reduced pressure in the turning area can be reduced at least to a level which is not dangerous. The recess, which is disposed in a free area between two sheets resting on the storage drum, may be sufficiently extensive, in the circumferential direction of the storage drum, for a direct passage between an area of the sheet-fed rotary printing machine which lies above the roll nip formed between the turning drum and the storage drum and the reduced-pressure area to be formed for a brief period in a specific rotation-angle position of the storage drum, so that ambient air can flow and/or blast/compressed air can be blown directly into the reduced-pressure area via the recess which is open toward the outer lateral surface of the storage drum. In addition, or as an alternative, air can be sucked or blown out of the inner chamber of the storage drum, which may be connected to a blast-air/compressed-air supply device, into the reduced-pressure area via the passage orifice. In another embodiment, air is fed to the reduced-pressure area via the channel that is connected to the environment and/or interacts with a blowing device.
In another embodiment, the device is distinguished by the fact that the turning drum is eccentrically mounted and the holding device is disposed on this drum in such a manner that at the very moment at which the sheet rear edge is picked up by the holding device, a free space is formed between the turning drum and the storage drum. With the aid of the free space which is left clear between the opposite outer lateral surfaces of the storage drum and the turning drum, it is possible to produce a flow connection between the environment and the reduced-pressure area delimited by the sheet to be turned, the turning drum and the storage drum. The free cross section of flow of the free space is at least large enough for it to be possible for a sufficient amount of air to flow or be introduced into the reduced-pressure area during the turning operation, so that in this area the pressure reduction which is formed by the entrained air when the sheet is turned can be reduced to a level which is not dangerous and in this way it is possible to prevent the next sheet, which is resting on the storage drum, from being lifted off. Ambient air can preferably flow in through the free space of its own accord. It is also possible for blast air to be blown into the turning area of the sheet through the free space.
In an additional embodiment, the device is distinguished by the fact that the turning drum, at least on its outer side, hasxe2x80x94as seen in cross sectionxe2x80x94at least one flattened section whichxe2x80x94as seen in the direction of rotation of the turning drumxe2x80x94is disposed downstream of the holding device, which is provided on the turning drum, for the sheet rear edge. The flattened section, which is formed by at least one planar or substantially planar area made on the outer side of the turning drum serves to produce a free space between the turning drum and the storage drum in a defined rotational position of the turning drum, through which free space air can be introduced into the turning area of the sheet which has been taken hold of by the holding device of the turning drum. In this case too, it is possible to reliably prevent the next sheet, which is held on the circumference of the storage drum, from being lifted off in the turning area by an excessive pressure reduction.
In accordance with another embodiment, the device is distinguished by the fact that compressed air can be introduced laterally into the reduced-pressure area by at least one fixedly disposed blowing device. The compressed air or blast air may, for example, be blown directly into the reduced-pressure area orxe2x80x94in an advantageous embodiment of the turning devicexe2x80x94may be blown into a distributor chamber which is provided in the storage drum and is in preferably direct communication with the reduced-pressure area via at least one flow path.
In an advantageous exemplary embodiment of the turning device, the storage drum may simultaneously also serve as an impression cylinder or may be formed by an impression cylinder.
With the foregoing and other objects in view there is further provided, in accordance with the invention, a sheet turning device for a sheet-fed rotary printing machine. The sheet turning device is formed of a storage drum for handling at least two sheets and has at least one holding device for each of the sheets, a lateral surface, at least one open-edged recess formed therein, at least one inner chamber formed therein, and at least one passage formed therein and connects the inner chamber of the storage drum to the lateral surface. A turning drum is disposed downstream of the storage drum and has at least one holding device for engaging a rear edge of a sheet of the sheets to be turned. An operation of detaching the sheet to be turned from the storage drum and carrying it along by the turning drum leads to a formation of a pressure reduction in a reduced-pressure area formed between the sheet to be turned, the storage drum and the turning drum. Via the open-edged recess and the passage of the storage drum air can be introduced into the reduced-pressure area.
In accordance with an added feature of the invention, the air can be at least one of sucked from and blown into the reduced-pressure area via the passage.
In accordance with an additional feature of the invention, the reduced-pressure area is in communication with the lateral surface of the storage drum via the passage. The lateral surface of the storage drum has at least one of at least one further channel and at least one further passage orifice formed therein connecting the inner chamber of the storage drum to an area of the lateral surface on which a subsequent sheet is resting.
In accordance with another feature of the invention, an air supply is connected to the passage and is selected from the group consisting of a compressed-air supply device, a blast-air supply device and the environment.
In accordance with a further added feature of the invention, the holding device of the storage drum is disposed in the open-edged recess.
In accordance with a further additional feature of the invention, the turning drum has an inner chamber formed therein, a lateral surface, and at least one passage orifice formed therein and connecting the inner chamber to the lateral surface of the turning drum, and through the passage orifice air can be at least one of sucked from and blown into the reduced-pressure area.
In accordance with another added feature of the invention, the passage is formed of a channel connected to a passage orifice.
With the foregoing and other objects in view there is additionally provided, in accordance with the invention, a sheet turning device for a sheet-fed rotary printing machine. The sheet turning device is formed of a storage drum for handling at least two sheets and has at least one holding device for each of the sheets; and a turning drum disposed downstream of the storage drum and has at least one holding device for engaging a rear edge of a sheet of the sheets to be turned. An operation of detaching the sheet to be turned from the storage drum and carrying it along by the turning drum leads to a formation of a pressure reduction in a reduced-pressure area formed between the sheet to be turned, the storage drum and the turning drum. The turning drum is an eccentrically mounted turning drum and the holding device of the turning drum is disposed on the turning drum such that at a moment at which the rear edge of the sheet is engaged by the holding device of the turning drum, a free space is formed between the turning drum and the storage drum.
In accordance with an added feature of the invention, the storage drum has an outer lateral surface; and the turning drum has an outer lateral surface and is configured such that, in a defined rotation-angle position of the turning drum, a distance between the outer lateral surface of the turning drum and the outer lateral surface of the storage drum is virtually zero.
In accordance with an additional feature of the invention, the turning drum has an outer lateral surface with at least one flattened section and the holding device of the turning drum is disposed on the flattened section.
In accordance with another feature of the invention, the turning drum has a given length and the flattened section extends over an entire length of the given length.
With the foregoing and other objects in view there is additionally provided, in accordance with the invention, a sheet turning device for a sheet-fed rotary printing machine. The sheet turning device is formed of a storage drum for handling at least two sheets and has at least one holding device for each of the sheets; and a turning drum disposed downstream of the storage drum and has at least one holding device for engaging a rear edge of a sheet of the sheets to be turned. An operation of detaching the sheet to be turned from the storage drum and carrying it along by the turning drum leads to a formation of a pressure reduction in a reduced-pressure area formed between the sheet to be turned, the storage drum and the turning drum. The turning drum has an outer side with at least one flattened section which, as seen in a direction of rotation of the turning drum, is disposed downstream of the holding device of the turning drum.
With the foregoing and other objects in view there is additionally provided, in accordance with the invention, a sheet turning device for a sheet-fed rotary printing machine. The sheet turning device is formed of a storage drum for handling at least two sheets and has at least one holding device for each of the sheets and a turning drum disposed downstream of the storage drum and having at least one holding device for engaging a rear edge of a sheet of the sheets to be turned. An operation of detaching the sheet to be turned from the storage drum and carrying it along by the turning drum leads to a formation of a pressure reduction in a reduced-pressure area formed between the sheet to be turned, the storage drum and the turning drum. A blowing device supplying air being at least one of compressed air and blast air that can be introduced laterally into the reduced-pressure area is provided.
In accordance with an added feature of the invention, the storage drum has a lateral surface with at least one recess formed therein. The recess is open towards the lateral surface and into which the air can be blown laterally by the blowing device, and in a defined rotation-angle position of the storage drum there is a flow connection between the recess and the reduced-pressure area.
In accordance with an additional feature of the invention, the blowing device has a plurality of blowing nozzles disposed on opposite sides of the storage drum and are oriented such that with respect to one another that their streams of air come into contact with one another in at least one of the reduced-pressure area and in the recess.
In accordance with another feature of the invention, the storage drum has a length and the recess extends over the length and rotates together with the storage drum.
In accordance with a further feature of the invention, an introduction of the air into the reduced-pressure area is controlled on a basis of rotation angle.
In accordance with a concomitant feature of the invention, the storage drum simultaneously functions as an impression cylinder.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in devices for turning sheets in a sheet-fed rotary printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.